Fusion Drive quick look: Our predictions confirmed!

Core Storage-powered tiering technology gives you one disk to rule them all.

Ars has its Fusion Drive-equipped Mac Mini in hand, and I've begun digging into it. We'll do a full review next week, but it's immediately obvious that many of the suppositions about Fusion Drive were correct: the technology uses Core Storage to bind together the physical hard disk drive and the physical solid state drive into a single volume. The aggregate capacity is the sum of the two, minus system partitions for booting and recovery.

Contrary to rumor, Finder sees but a single drive, as does the graphical version of Disk Utility:

There are three disk devices exposed: disk0, the SSD; disk1, the HDD; and disk2, the Core Storage volume. The two physical disks have several partitions, but the third device has only the single Apple_HFS partition listed.

The last device, disk2 is the Fusion Drive. Interestingly, it identifies itself as a solid state disk (see near the bottom), which likely affects OS X's treatment of it with respect to hotfile clustering (OS X's sort-of defragmentation scheme).

Running diskutil again and this time requesting info about available Core Storage volumes yields what we've been looking for: Fusion Drive made of Core Storage.

Specifically, the two physical devices (the HDD and the SSD) are grouped together into a single Logical Volume Group, which in turn contains a Logical Volume Family made up of a single Logical Volume. That Logical Volume, disk2, is our Fusion Drive.

OS X is definitely aware that it has two disks, though. Even though only disk2 is visible, System Information knows that there's both an SSD and an HDD in there.

I haven't kept up on this, but is a Fusion Drive the same as a hybrid drive or do they differ in some technical respect?

A Hybrid drive is a spinning disk with a small SSD cache on board (32 or 64 GB). Fusion drive is 2 separate physical drives being combined into one volume.

In addition, cache is temporary storage, with the original file still stored on the hybrid's HDD. The HDD is activated in all write operations. With Fusion, the SSD is part of the main storage. OS X keeps the most-used files on the SSD, and less-used files on the HDD. OS X dynamically moves files from SSD to HDD, and vice versa, during idle periods to continually optimize this setup.

I haven't heard about this before, but at first glance it seems like a bad idea. I want to be really specific about what data I keep on my SSD and what data I want on my HDDs. What advantages are there to this Fusion Drive Approach? How good is it about prioritising data to the SSD and maintaining the SSD's lifecycle by minimising unnecessary writes?

What I've always done is mount my HDDs as directories under my OS install which is on my SSD. That way I can be quite granular about which programs will launch from the SSD and which can be relegated to the HDDs. Media is all obviously relegated to HDD land. Is the Fusion approach a significant improvement over this approach? Also, how does the fusion drive behave with a single drive failure? Is data readily recoverable from the remaining drives or does the loss of a single drive break the filesystem like older JBOD implementations?

I imagine some of the questions will be answered in the full review, but I have to admit at this point the Fusion approach seem like a solution looking for a problem to me.

I haven't kept up on this, but is a Fusion Drive the same as a hybrid drive or do they differ in some technical respect?

This is not the same as a hybrid or caching drive. This is full tiered architecture, and it intelligently monitors activity, and manually moved data between the 2 volumes. It's ALSO been confirmed this is not file-level, but block level or some other construct, as super-large fuiles will only have some parts migrate between volumes, and definitively databases and war files used by things like iPhoto or Aperature only move active items in the database not the entirety of it. This is clearly a tiered storage system managing the data directly, not a cache where it;s simply written to the fast storage only long enough to be copied to slower disk and purged from the cache. There may still ALSO be a simulated cache system in operation, a portion of the SSD reserved for sinulating that process, but we do not know yet. We do know this is not intel SRT, but something even more advanced and flexible both, and software based, not firmware as it does work on older macs too.

cc bcc wrote:

Does the boot partition contain all system files or just enough to be able to boot from the fusion drive?

Per Apple, yes, the OS installation initially lands 100% in the SSD, as will virtually any file you write pending there's still some room (we have no idea if CoreStorage pads any space specifically for that purpose or not). When idle, it begins moving things about so over time, unused OS components (drivers, printers, apps, services, etc) will migrate off the SSD, but, it will only do that as needed. (store less than 128 total GB and it will all stay on the SSD).

cc bcc wrote:

If you reinstall OS X does the installer ask to combine the ssd and hdd into a fusion drive?

My guess is, the latest OS X installer will collect volume information from TimeMachine and do that, yes. That's just a guess though. To initially create it on an unsupported machine takes manual efforts, and it's as yet unclear if tools to do that ship with the supported machines.

backups, restores, and encrpption: Based on what we know of how the OS reads information vs the underlying system, this should work perfectly with full-disk encryption. It will work with home folder encryption I'm guessing only when the specific user is logged in as it would not have access to the other user's folders, but, then again. in fact, how it works with multi-user systems remains to be seen. Backups, whether time machine or 3rd party won't be effected, though restoring shoudl in effect treat writing the data as new data and will be unlikely to restore bits to the right drives, but over a short time they'll muigrate back in place on their own. Given the software specific both file and block natures of this system, it;s possible TM may in fact store the required bits to know where to put a file back, but that's unlikely as it would require this system to maintain a very large fast database that's also backed up, or changes to HFS+ itself to support it, meaning the performance data would become user accessible which in my opinion would be unsave and unrelaible, so I suspect restores will simply replace the OS first (on the SSD0 then fill it up with data from the backup untuil full and move to the HDD. It;s possible files by type may be considdered, with media or files in certain folders automatically choosing HDD or SDD, but that's a bit more complex than I suspect a first pass would handle.

Older Macs: Yes, this works on all macs tested capable of supproting dual drives per other sites. If you mac can run 10.8.2, it should support fusion. There may be specific drive hardware requirements that are unspecified (firmware supprot or advanced SATA features some cheap drives may not posess, certain types of SSDs, etc, don't know yet).

So, for science, are you going to corrupt the SSD, and see if you lose all the data on the whole drive, or just what was on the SSD?

RAID0 ho!

This is a single LVM. Yes, if any of the drives in the LVM are lost the data is lost. That said, SSD+HDD shoudl have within 1-2% MTBF vs a HDD alone. The quality of SSD and padding it contains for failed blocks over time will be important, but, it;s a mac, you have Time machine, and i seriously doubt any tinkerers are lacking using it for important data, and that higher-end purchasers are also skimping on backups.

If you look at the partitioning section of Disk Utility, does it allow you to see both parts? Or would you have to go command line to break the Fusion Drive setup? I was expecting that Disk Utility would show the drive similarly to a software RAID.

Again Apple passing off old tech as something "new and magical" and of course the fanbois swallow it whole like the greedy hungry animals they are!

This is the first known appearance of true tiered storage technology in a commercial PC or laptop. Also, this is clearly determined NOT to be SRT from intel, is not a basic caching system like hybrid drives, and is also not strictly block OR file level in nature, it is a hybrid of several systems similar only generally in some and unique in many ways. This is not some old tech passed off as new, many technical sites have expressly confirmed they're not even sure yet WHAT it really is, they're just certain it;s both new and in-house grown.

I'm no Fanboi, I'm an analyst, and I think I won;t be alone here in saying, trolls are not welcome on Ars Technica, please take your biased and ill-informed comments to one of those lesser blogs that claim to be tech sites.

I haven't heard about this before, but at first glance it seems like a bad idea. I want to be really specific about what data I keep on my SSD and what data I want on my HDDs. What advantages are there to this Fusion Drive Approach? How good is it about prioritising data to the SSD and maintaining the SSD's lifecycle by minimising unnecessary writes?

What I've always done is mount my HDDs as directories under my OS install which is on my SSD. That way I can be quite granular about which programs will launch from the SSD and which can be relegated to the HDDs. Media is all obviously relegated to HDD land. Is the Fusion approach a significant improvement over this approach? Also, how does the fusion drive behave with a single drive failure? Is data readily recoverable from the remaining drives or does the loss of a single drive break the filesystem like older JBOD implementations?

I imagine some of the questions will be answered in the full review, but I have to admit at this point the Fusion approach seem like a solution looking for a problem to me.

Yes, this is an improvement over file janitoring.

Unless your time is completely worthless, that is.

I'm guessing that drive loss will lead to the loss of files on the failed drive. Loss of either drive will probably necessitate a restore from backup.

How is this different than a Seagate Momentus or the SSD drives that comes with software that does this automaticly?

edit:

OK, it's different because it's two different drives. But it's still old tech. You can purchase SSD drives that does this automaticly. Anandtech reviewed a 128GB, with 60GB usable (to save on flash), that did exactly precisely this.

But it didn't come in a Mac, and he didn't write an article about the fact that the was going to write an article about it.

If you have an SSD drive and a normal HD, you can just install some software that does it for you. Shrug.

Well the hybrid drives like the seagate one have a higher MTBF than a standard spinning disk, placing it at or near an enterprise level sas drive. Because everything is handled in the device (drive) it will spin down the drive when it does not need it... and move common files to the 8GB SLC NAND.

The use of SLC in the seagate drives is a good move IMO and part of the increased MTBF...

We will really have to see how longevity plays out in the Apple Fusion Drive... MLC could play a role in this...

All this being said the MTBF for a fusion drive will be worse than that of a single spinning disk, because it includes both a spinning drive and a SSD combined with LVM... leaving a couple points of failure that would destroy the entire volume. But this is just my opinion...

But it didn't come in a Mac, and he didn't write an article about the fact that the was going to write an article about it.

If you have an SSD drive and a normal HD, you can just install some software that does it for you. Shrug.

- Isn't there an "ignore Apple stories" option somewhere on the site? Rarely does Apple do something that was completely impossible before its implementation. But it's still news that this tech is available as an option on consumer computers.

- The way that this works is interesting to many of us. Core Storage! Best of all, it looks to be a baked into Mountain Lion—and I'd be much happier relying on a scheme like this that's part of the OS than one that's implemented in 3rd party software.

So, for science, are you going to corrupt the SSD, and see if you lose all the data on the whole drive, or just what was on the SSD?

RAID0 ho!

"Test to failure" is *ALWAYS* on my list of things to do to new hardware

While you're testing things like that can you also see what happens if you try to put more than one extra partition on the drive, like for windows or linux. I know that the graphical version of diskutiltiy shouldn't allow it but what about the command line version?

I haven't heard about this before, but at first glance it seems like a bad idea. I want to be really specific about what data I keep on my SSD and what data I want on my HDDs. What advantages are there to this Fusion Drive Approach? How good is it about prioritising data to the SSD and maintaining the SSD's lifecycle by minimising unnecessary writes?

What I've always done is mount my HDDs as directories under my OS install which is on my SSD. That way I can be quite granular about which programs will launch from the SSD and which can be relegated to the HDDs. Media is all obviously relegated to HDD land. Is the Fusion approach a significant improvement over this approach? Also, how does the fusion drive behave with a single drive failure? Is data readily recoverable from the remaining drives or does the loss of a single drive break the filesystem like older JBOD implementations?

I imagine some of the questions will be answered in the full review, but I have to admit at this point the Fusion approach seem like a solution looking for a problem to me.

This will, after stabilizing your data set, ber within a few percent average performance vs an SSD only solution, but will allow you to also benefit from large storage concurrently. This is tried and true enterprise architecture. If you explicitly want to manage your storage, you absolutely have that option, just break the LVM and set it up as 2 drives, and feel free. The advantage here is a contiguous voolume instead of 2, and we can pretty mcuh guess than any mental rules you might have tfor how to prioritize are in there. More importantly, this works at the sub-file level, which you cannot, meaning the database headers and recent or active information in a file like the Aoperature library file could be on the SSD while the rest of the giant file is on HDD, allowing Aperature to load it;s database at SSD speeds, and access recent shoots, but, does not require the whole thing on SSD to do so.

This type of techology is the difference between a million dollar SAN and a 100K SAN, and now for virtually no premium at all we have a very similar system available to laptops and desktops. This is what we've been waiting for in storage for personal computers for 15 years. You can only manage data by folders, use cases, and files, this can manage data much more granularly, while still providing a unified vertual file system. it's also likely to have all the benefits of a cache system as well, using a small portion of the SSD for that, though we're not certain yet.

Come on, of course it's fine and normal for Ars to review iMacs, just like any other hardware. But a pre-article about an article about something that you could just walk into a store and purchase 8 months ago from a mainstream manufacturer?

You got voted down probably because you were being abrasive and also because you were wrong.

I haven't kept up on this, but is a Fusion Drive the same as a hybrid drive or do they differ in some technical respect?

This is not the same as a hybrid or caching drive. This is full tiered architecture, and it intelligently monitors activity, and manually moved data between the 2 volumes. It's ALSO been confirmed this is not file-level, but block level or some other construct

Now I'm not belittling FusionDrive as if you see my previous posts I'm a huge mac fan. It's just not that different and I bet Apple got tired of asking intel to port SRT to OSX. Kind of cool that it's built on top of LVM too.

Come on, of course it's fine and normal for Ars to review iMacs, just like any other hardware. But a pre-article about an article about something that you could just walk into a store and purchase 8 months ago from a mainstream manufacturer?

because that link is to a Cache drive, which is NOTHING LIKE FUSION AT ALL if you bothered to read any of the data available at this or another blog. The Corsair drive is simply a not-permanatly-connected-cache drive relying on a simple driver, and some algorithms and extra software from Nvelo to keep current files on the SSD. it;s more advanced than say, momentus, but it is not Fusion. It handles file-level-only. Fusion is working inside files.

With Corsair, your entire aperature library file would either need to be on the SSD, or not. With Fusion, only the parts of the library used as a database, and active working images would be on the SSD, with the rest on HDD, smealessly.

Fusion apparently also works with any drives, not specific ones designed for this system. nvelo's system only works with a limited set of manufacturers SSDs they term "cache SSDs" and which come at significant premiums in price vs drives of the same capacity readily available.

I'm confused, all this output dump tells me is that both drives form a CoreStorage RAID0-ish volume group, similar to what I did with LVM on Linux many years ago. So far so good, but where does it tell the OS to do this fancy tiering we've discussed about earlier?

How would one do a clean install of OSX on a fusion drive? Just curious because when a new version of OSX (i.e. 10.9) comes a long I prefer to do a clean install on my Mac. Hopefully this won't be too complicated.

I was just thinking about it as software that made the SSD and HD look like a single drive, and managed which data would be on the SSD (as I recall, the Dataplex also does more than this, but it looks like I was to hasty according to the replies I get).

Again Apple passing off old tech as something "new and magical" and of course the fanbois swallow it whole like the greedy hungry animals they are!

Thanks for the trolling, you're always good for a laugh. I honestly wonder sometimes if you are putting out a straw man just to say something negative, or if you are actually as stupid as your comment makes you sound.

Back to the article though, looking forward to the review next week. I am looking to pick up a Mac mini (the quad core version, it's what I've been waiting for on the mini) and I'm on the fence about the Fusion Drive. If it does a good job of speeding things up I think I'll have to lean in that direction.

I haven't kept up on this, but is a Fusion Drive the same as a hybrid drive or do they differ in some technical respect?

This is not the same as a hybrid or caching drive. This is full tiered architecture, and it intelligently monitors activity, and manually moved data between the 2 volumes. It's ALSO been confirmed this is not file-level, but block level or some other construct

Now I'm not belittling FusionDrive as if you see my previous posts I'm a huge mac fan. It's just not that different and I bet Apple got tired of asking intel to port SRT to OSX. Kind of cool that it's built on top of LVM too.

There's 2 types of caching on the market today. Read/write caching (as momentus and others do it, the cache is in no way part of the volume, whole files are written to the cache so they can be more quickly written and paged to HDD as time permits, and to take fuerther advantage of NCQ. The other is caching like Nvelo, which is a drive linked (using sofware, not an LVM, the OS still sees 2 volumes), and which virtualizes a file system on top, and moves only whole files. A database in Nvelos solution has to entirely live on SSD or HDD, in Fusion parts of it can be in both concurrently as it is working at the sub-file level (part intelligently understanding library files natively, part just block level migration and filesystem table manipulation (forced fragmentation for oerfornmance enhancement).

SRT is hardware-only and requires specuific chipset support. Caching drives require software that sits ON the OS. This uses OS specific advantages for dramatically more flexibility and performance, and also is backward compatible to virtually any SATA based MAC (so long as it runs 10.8.2 or higher).

Please edit the original article to show more "correct" diskutil output from the command line in terms of formatting.

I love the info and it's great to get this out in such a timely fashion, but it's very hard to read. Whereas the diskutil output is actually formatted nicely and well spaced, I think your CMS is just clobbering this somehow.

Lee Hutchinson / Lee is the Senior Reviews Editor at Ars and is responsible for the product news and reviews section. He also knows stuff about enterprise storage, security, and manned space flight. Lee is based in Houston, TX.